Vehicles are currently being manufactured with airbag devices. Typically airbags have been provided in the steering wheel and the instrument panel for frontal protection in a crash. Additionally side curtain airbags are provided that can assist in a crash or side impact. Side curtain airbags generally deploy from the top of the vehicle and cover the window areas to provide some head and upper body protection. Other airbags may be provided such as knee bolsters and the like to protect various parts of a vehicle occupant's body during a crash. Another type of airbag is included in a seat mounted side airbag module that provides protection for a vehicle occupant in a side impact.
While all airbag systems provide protection there have been challenges with each type of airbag system that have resulted in numerous innovative solutions. A particular challenge for seat mounted side impact airbags is that the airbag when inflated is either too soft or too rigid. It has been determined that to provide the proper protection for the lower portion of the vehicle occupant's body in the pelvic region requires a stiffer airbag while the upper region of the airbag that encounters the thoracic region of the vehicle occupant needs to be a softer. Several solutions have been proposed to meet this challenge. EP 999101 A1 and in U.S. Pat. No. 5,803,485 A provide a single inflator that inflates two separate airbags. These separate airbags can be inflated such that both the upper thoracic region and the lower pelvic region of a vehicle occupant are adequately protected. US 2005/0062266 A discloses an alternative having one airbag with a separate pelvic engaging inflation chamber and a separate thoracic engaging inflation chamber employed where the gas flow rates are tunable to provide variation within the inflation chambers.
While these solutions provide protection for a vehicle occupant, it has been determined that such systems increase certain levels of complexity with regards to the inflation chambers. Obviously a tuned, two separate airbag system provides the ability to isolate the two bags and provide separate filling upon inflation, however, it was preferred that a single airbag accomplish this task. US 2005/0062266 A tries to achieve this, however, there is no complete isolation of the two inflation chambers such that the gas flow cannot be mixed. As such the bleed through of gasses from one inflation chamber to the other creates a variable in the ability to tune the airbags. While differences in inflation pressures can be achieved using such a device an improvement is needed.